When you think of mountains, you probably think of tall rocky edifices, soaring to great heights, like the Himalayas, the Rockies, the Andes, etc. And all of these mountains are due to modern plate tectonics, with plates running into one another and either uplifting vast tracts of land or subducting down and giving rise to high-reaching volcanic peaks. But Earth didn’t always have the plate tectonics it does today.

New research published in Geophysical Research Letters provides geochemical evidence that continental rocks in the Proterozoic era, about 1.8 billion to 850 million years ago, weren’t thick enough for the kind of mountain building we see in the recent geologic past. In fact, it was less than 40 kilometers thick and very hot compared to today’s continental crust. However, these same rocks had signs of metamorphic minerals — minerals that formed under similar types of pressures and temperatures that signify mountain building.

Despite the thin, hot crust, mountain formation was possible as bits of young, relatively weak crust slid past itself, with glancing blows rather than the head-on collisions we see in places like India today. Those glancing blows were enough on a geologic time scale to cause the formation of lower, flatter mountain ranges than I mentioned earlier. Lead author Christopher Spencer sums the research up: Mountains during the Proterozoic were different from mountains at any other time in Earth’s history.

More Information

Extinct Style of Plate Tectonics Explains Early Earth’s Flat Mountains (Eos)

“Enigmatic Mid-Proterozoic Orogens: Hot, Thin, and Low,” Christopher J. Spencer, Ross N. Mitchell, and Michael Brown, 2021 July 30, Geophysical Research Letters